A zirconia sintered body having a small amount of Y2O3 (yttria) solid-solubilized as a stabilizer, has high strength and high toughness and thus is widely used as a material for a mechanical structure such as a cutoff tool, a die, a nozzle or a bearing, or as a biomaterial such as a dental material. In recent years, a zirconia sintered body having high strength has been used as a dental material, and in order to bring its color tone close to the color tone of natural teeth, it has been common to laminate another material on the surface of the zirconia sintered body and to adjust its aesthetic properties. However, along with the progress of utilization of the zirconia sintered body in the dental field, there has been an increasing demand for a zirconia sintered body which is useful as it is as a dental material without necessity to laminate another material.
In order to use a zirconia sintered body as it is as a dental material, both of translucency and coloration (color tone) are required. Heretofore, a zirconia sintered body having an ivory color close to natural teeth has been disclosed (e.g. Patent Document 1). In this Patent Document, addition of Pr6O11 and ZnO to a zirconia sintered body is essential, and there is no disclosure about translucency.
Further, a zirconia sintered body having a sintered body density of 99.8% and having translucency with a composition comprising 3 mol % of Y2O3 and 0.25 wt % of Al2O3 (alumina) has been disclosed (e.g. Patent Documents 2 and 3). However, the zirconia sintered body disclosed therein is one containing no colorant, and thus, heretofore, a zirconia sintered body which is colored and yet has high translucency, has not been in existence.
Patent Document 4 discloses a translucent zirconia sintered body colored to have a yellowish color tone by addition of Fe. By imparting a yellowish color tone, a color tone approximate to natural teeth was obtainable, but it was inadequate in a reddish or blackish tinge. By laminating another material on its surface to bring the color tone close to natural teeth, it was possible to use it, but it was not possible to use it as it is, since the difference in color tone from natural teeth was large.
By virtue of its high strength, a zirconia sintered body has been used mainly as a structural member or grinding media. However, from its beautiful surface gloss after mirror polishing, its application to a decorative member or an exterior package for electronic material is now expected. In order to meet with such broadened application, a colored zirconia sintered body which is excellent in aesthetic properties and has high strength, is desired.
Heretofore, as pink-colored zirconia sintered bodies, ones employing various additives have been proposed, but there has been none which has necessarily sufficient aesthetic properties. Particularly, zirconia has had such a problem that a colorant is hardly uniformly solid-solubilized therein, as compared with alumina, whereby a clear color tends to be hardly obtainable, or that the additive amount is relatively large so that it can hardly be sintered, whereby the properties of the sintered body, particularly the mechanical strength, tend to deteriorate.
Heretofore, the following ones have, for example, been proposed as pink-colored zirconia sintered bodies.
Patent Document 5 discloses a pink-colored zirconia sintered body having from 0.5 to 2 mol % of Er2O3 and from 0.1 to 0.6 mol % of ZnO incorporated to zirconia containing a stabilizer. Such a sintered body is one containing zinc oxide and further another coloring assistant, as essential components.
Further, Patent Document 6 discloses a pink-colored sintered body comprising from 2 to 5 mol % of Y2O3 as a stabilizer, and from 1 to 3 wt % (from about 0.3 to 0.9 mol %) of Er2O3.
Further, Patent Document 7 proposes a zirconia sintered body comprising from 0.6 to 1.2 mol % of Y2O3 as a stabilizer, and from 1.4 to 1.8 mol % of Er2O3.